Electrical machines and the respective foundations have common natural system frequencies.
Systems composed of an electrical machine and foundation and whose natural system frequencies correspond to the excitation frequencies as rotational frequency and/or, preferably, in the case of 2-pole machines to twice the line frequency, lead to considerable vibration problems. These vibration problems are expressed in excessively high material stresses which lead to material damage if the permissible stress values of the material are exceeded. Moreover, large-scale functional impairments occur when certain deformation limits are exceeded which lead, for example, in the case of rotor vibrations of electric motors, to a bridging of the play between the rotor and housing. Motors which exhibit no vibration objections in acceptance tests where "hard" foundations are present can nevertheless lead to vibration problems for customers with "soft" foundations. It has so far been possible to conform to the vibration requirements of the standards and the customers only by methods which are complicated in terms of design and time-consuming such as, for example, by making changes to the foundation or the rotor (shaft diameter).
A further possibility of meeting these requirements consists in changing the bearing, for example, by changing the bearing span, by using sliding bearings instead of rolling bearings, or vice versa. These approaches entail high costs and lead to unplanned modification periods which lead to a loss of production for the customer.